I purchasrd Advantage 11 for large cats, 6 pack, Dec 27, 2017. Feb 6, 2018, received refund & Amazon said "manufacturer" reimbursed for safety issues. I used on 2 cats Jan 20. Spoke with Dr Hall at Bayer Feb 6 and he said Amazon contacted them Jan 5, 2018 when they learned had counterfeit product & Bayer told them product WAS NOT purchased from them. Amazon rep told me mass email was sent Jan 15, 2017 supposedly to all customers who may have received "safety issue" product - I never received.